A preliminary investigation seems to indicate that this problems stems
from camlp4's quotations (*). Camlp4 views the "<<" string as the start
of a quotation and ">>" as its end. Moreover, if no ">>" is provided,
camlp4 will complain, reporting that a quotation is not terminated.

My first interpretation is that this is a camlp4 bug but some in-depth
understanding of camlp4 is needed to confirm that. I have thus contacted
Nicolas Pouillard (camlp4 guru) and will update this report with any
additional information.

Well, I have to made public apologies for the mistake in the previous note.
As explained by Nicolas Pouillard, the reported behaviour is indeed expected.

The idea is that quotations behaves here as strings would: when embedded
inside comments, they have to be properly closed (this behaviour is clearly
needed if you want to always be able to properly comment out strings or
quotations).

On the reported example, this means that the comment opened right after
"A" ends on the "*)" that follows the end of the quotation. A similar example
on strings is that the following program will print "abc":
let () = print_endline (* " ABC DEF *) " *) "abc"

The obvious conclusion is that this bug report is closed with no modification
on the code base. However, the next version of the manual will be enriched
with a note warning the Bisect user of possible camlp4 interactions.